Scientists say that omega-3 fatty acids in fish oil can help people with heart disease live longer. But until now, no one knew why omega-3 oils are so beneficial.

This is what coronary artery disease looks like. Plaque builds up inside the coronary arteries and blocks the flow of blood to the heart.

Coronary artery disease is one of the leading causes of death worldwide. Numerous studies show that cold water fish --salmon, tuna and other oily fish -- contain omega-3 fatty acids that can decrease the risk of this disease. But no one knew exactly why.

Dr. Ramin Farzaneh-Far at the University of California conducted a study to see if there might be a link between cellular aging and omega-3 acids. "The main result from our study is that patients with high levels of omega-3 fish oil in the blood appear to have a slowing of the biological aging process," Dr. Farzaneh-Far said.

Protective caps on the ends of chromosomes called telomeres, shown here in red, contain genetic material. As they shorten, cells age.

Dr. Farzaneh-Far and colleagues measured the length of telomeres in blood cells of 600 heart patients. They wanted to see if there was any association between the levels of omega-3 fatty acids and the change in telomere length over a period of time.

"Patients with the highest levels of omega-3 fish oils were found to display the slowest decrease in telomere length, whereas those with the lowest levels of omega-3 fish oils in the blood had the fastest rate of telomere shortening, suggesting that these patients were aging faster than those with the higher fish oil levels in their blood," Dr. Farzaneh-Far explained.

Dr. Farzaneh-Far says the results of his study support the American Heart Association's recommendation that heart disease patients with coronary artery disease have at least one gram per day of omega-3 fish oil.

Researchers used to think that only regular exercise and managing stress could keep telomeres healthy. But either eating fatty fish or taking omega-3 supplements can also be effective. At the most, Dr. Michael Roizen of the Cleveland Clinic says it will not hurt. "It's a risk free way of potentially extending lifespan and reducing disability," he said.

And omega-3 acids are not just for heart disease patients. Omega-3's have been associated with easing joint inflammation, slowing memory decline, and reducing macular degeneration, the most common cause of blindness in the elderly.